vinyl dye is cheap for a little bottle, under 10 bucks. I dont know of too many fiberglass interiors, if its the smooth look your looking for that can be achieved through normal paints. A good sanding of the plastics, good paint and clear coat, a final rub with a wax bar will make them smooth and shiny!
Unfortunately it's not exactly that simple with our interiors since the dash has a texture. What that means is you'll need to either use LOADS of filler primer, sand your ass off, or use bondo or fiberglass resin. However SEM makes a plastic paint that chemically bonds to the dash. Is a bit easier than dying if you wanted to go the DYI route. I will be doing this over the course of the winter hopefully.